Amphimixis and Nutritive Irregularities in Germs 195 
not prevented from passing to descendants by the con- 
jugation of this individual with others which do not 
possess any such variations, but are only diluted, so to 
speak. Therefore all that is necessary is to suppose the 
struggle for existence to be more severe or to have a 
higher degree of selective capacity than that which would 
have been sufficient if there had not been sexual repro- 
duction. 
It is well known further that Weismann, in order 
to afford natural selection abundant and never failing 
material upon which to act, has made for himself a 
weapon of sexual reproduction, attributing to it a great 
fruitfulness in the constant production of new variations. 
But he seems to have been partly converted finally to the 
opposite view of the Lamarckians already mentioned, 
that sexual reproduction only contributes to securing the 
unity and constancy of the species. For, in order to ex- 
plain the production of a lot of fortuitous variations, 
he finally sought refuge in the unavoidable irregularities 
of nutrition in the germ plasm,)®? a thing which makes 
his hypothesis upon the biologic function of amphimixis 
quite superfluous. It may be merely noted here that when 
once one sees in amphimixis a cause tending toward the 
levelling of individual characters and consequently to- 
ward the fixity of the species, and thereby reducing by 
so much the probability that the selective capacity of the 
struggle for existence is alone sufficient, one must then 
feel so much the more strongly the necessity of discover- 
ing some cause of variation capable of acting simul- 
taneously and in the same way upon at least quite a 
large part of the individuals of the species, and of 
182Weismann: Das Keimplasma. P. 541—570. 
